diff --git a/event-internal.h b/event-internal.h
index f9de18ad..7388a597 100644
--- a/event-internal.h
+++ b/event-internal.h
@@ -158,6 +158,9 @@ struct event_changelist {
 #ifndef _EVENT_DISABLE_DEBUG_MODE
 /* Global internal flag: set to one if debug mode is on. */
 extern int _event_debug_mode_on;
+#define EVENT_DEBUG_MODE_IS_ON() (_event_debug_mode_on)
+#else
+#define EVENT_DEBUG_MODE_IS_ON() (0)
 #endif
 
 struct event_base {
diff --git a/evmap.c b/evmap.c
index b11ec3c9..cb28002a 100644
--- a/evmap.c
+++ b/evmap.c
@@ -264,6 +264,7 @@ evmap_io_add(struct event_base *base, evutil_socket_t fd, struct event *ev)
 	struct evmap_io *ctx = NULL;
 	int nread, nwrite, retval = 0;
 	short res = 0, old = 0;
+	struct event *old_ev;
 
 	EVUTIL_ASSERT(fd == ev->ev_fd);
 
@@ -300,6 +301,13 @@ evmap_io_add(struct event_base *base, evutil_socket_t fd, struct event *ev)
 		    (int)fd);
 		return -1;
 	}
+	if (EVENT_DEBUG_MODE_IS_ON() &&
+	    (old_ev = TAILQ_FIRST(&ctx->events)) &&
+	    (old_ev->ev_events&EV_ET) != (ev->ev_events&EV_ET)) {
+		event_warnx("Tried to mix edge-triggered and non-edge-triggered"
+		    " events on fd %d", (int)fd);
+		return -1;
+	}
 
 	if (res) {
 		void *extra = ((char*)ctx) + sizeof(struct evmap_io);
diff --git a/test/regress_et.c b/test/regress_et.c
index 98f3dcf2..87ecc5ba 100644
--- a/test/regress_et.c
+++ b/test/regress_et.c
@@ -149,7 +149,49 @@ test_edgetriggered(void *et)
 	evutil_closesocket(pair[1]);
 }
 
+static void
+test_edgetriggered_mix_error(void *data_)
+{
+	struct basic_test_data *data = data_;
+	struct event_base *base;
+	struct event *ev_et=NULL, *ev_lt=NULL;
+
+#ifdef _EVENT_DISABLE_DEBUG_MODE
+	if (1)
+		tt_skip();
+#endif
+
+	event_enable_debug_mode();
+
+	base = event_base_new();
+
+	/* try mixing edge-triggered and level-triggered to make sure it fails*/
+	ev_et = event_new(base, data->pair[0], EV_READ|EV_ET, read_cb, ev_et);
+	ev_lt = event_new(base, data->pair[0], EV_READ, read_cb, ev_lt);
+
+	/* Add edge-triggered, then level-triggered.  Get an error. */
+	tt_int_op(0, ==, event_add(ev_et, NULL));
+	tt_int_op(-1, ==, event_add(ev_lt, NULL));
+	tt_int_op(EV_READ, ==, event_pending(ev_et, EV_READ, NULL));
+	tt_int_op(0, ==, event_pending(ev_lt, EV_READ, NULL));
+
+	tt_int_op(0, ==, event_del(ev_et));
+	/* Add level-triggered, then edge-triggered.  Get an error. */
+	tt_int_op(0, ==, event_add(ev_lt, NULL));
+	tt_int_op(-1, ==, event_add(ev_et, NULL));
+	tt_int_op(EV_READ, ==, event_pending(ev_lt, EV_READ, NULL));
+	tt_int_op(0, ==, event_pending(ev_et, EV_READ, NULL));
+
+end:
+	if (ev_et)
+		event_free(ev_et);
+	if (ev_lt)
+		event_free(ev_lt);
+}
+
 struct testcase_t edgetriggered_testcases[] = {
 	{ "et", test_edgetriggered, TT_FORK, NULL, NULL },
+	{ "et_mix_error", test_edgetriggered_mix_error,
+	  TT_FORK|TT_NEED_SOCKETPAIR|TT_NO_LOGS, &basic_setup, NULL },
 	END_OF_TESTCASES
 };